A wireless IC tag is a non-contact type tag in which desired data is written in a memory circuit in a semiconductor chip and the data is read by using a radio transmission such as microwave.
As a method for providing a unique identification number to each wireless IC tag, Japanese Patent Application Laid-Open Publication No. 2002-184872 (Patent Document 1) discloses a method in which a random number is generated in advance by a program to generate an identification number, and contact holes and through holes are formed in a memory circuit by using an electron beam writing method in a semiconductor wafer diffusion process so as to write the identification number in accordance with the presence of the contact holes and through holes.
Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2002-184872